The present invention generally relates to cellular communication systems, and, more particularly, to base stations used in cellular communication systems.
A cellular communication system includes an internet protocol (IP) gateway, a mobile switching center (MSC), home location registers (HLR), base station controllers (BSC), base transceiver stations (BTSs), and multiple user equipments (UEs). A BTS facilitates communication between the UEs and the MSC over a cellular network, and communicates with the IP gateway or a serving gateway (SGW) for providing IP-based network services from a core network to the UEs serviced by the BTS. The core network can be a packet-switched core network. The term BTS in the GSM standard corresponds to a Node-B in the third generation (3G).
The third generation partnership project (3GPP) introduces a long term evolution (LTE) system as an effective solution to the increasing performance requirements of mobile broadband communications. The LTE radio interface and radio network architecture ensures a high data transfer rate, reduced latency, data packet optimization, and improved system capacity and coverage. The LTE system offers an evolved universal terrestrial radio access network (E-UTRAN) as an air interface. The E-UTRAN includes several evolved Node-Bs (eNodeBs) that are also referred to as base stations or access points and correspond to the BTS of the cellular communication system. The eNodeBs are distributed across multiple cells, where each cell typically has one eNodeB. Each eNodeB communicates with multiple UEs located within the coverage area of a cell.
Every eNodeB includes a base station sub-system for transmitting and receiving radio-frequency (RF) signals to and from the UEs. The base station sub-system includes a baseband unit, an RF transceiver, and an antenna. The baseband unit modulates a carrier wave by changing one or more characteristics of the carrier wave, viz. amplitude, frequency, and phase, based on in-phase and quadrature-phase (I/Q) samples generated by a layer 1 (L1) processor included in the baseband unit. The RF transceiver transmits the modulated carrier wave on a transmission medium using the antenna. The transmission medium is divided into multiple communication channels based on available RF range. Communication channels for communication from the eNodeB to the UEs are referred to as downlink communication channels. Communication channels for communication from the UEs to the eNodeB are referred to as uplink communication channels. The uplink and downlink data plane communication between the eNodeBs and the UEs is enabled by a user plane protocol stack that can be divided into layer 1 (L1) and layer 2 (L2), respectively.
FIG. 1 illustrates a conventional base station sub-system 100 that includes an RF transceiver 102, an antenna 104, and a conventional baseband unit 106 connected to the RF transceiver 102, which is in turn connected to the antenna 104 for transmitting the modulated carrier wave (i.e., a “high-power RF signal”). The base station sub-system 100 is included in a conventional eNodeB (not shown) that communicates with multiple UEs in a cellular network (not shown).
The RF transceiver 102 includes an RF integrated circuit (RFIC) 108 and a power amplifier 110. The baseband unit 106 includes a system memory 112, a L1 sub-system 114 that includes a hardware accelerator 116 and a first processor 118, a second processor 120, a shared memory 122, and a direct memory access (DMA) system 124.
The system memory 112 is used to store downlink data packets that are received from a core network, which is a packet switched IP network (not shown). The system memory 112 could be an external storage device that is connected to the baseband unit 106 as a peripheral device.
The second processor 120 is connected to the system memory 112 for receiving the downlink data packets. A L2 processing agent 126 runs on the second processor 120. The L2 processing agent 126 includes a data plane processing module 128 and an air interface scheduler 130.
The data plane processing module 128 performs L2 processing of the wireless protocol stack. The data plane processing module 128 receives the downlink data packets from the system memory 112 and processes them to generate control data and downlink transport blocks (TBs). The downlink data packets are transmitted from the system memory 112 to the data plane processing module 128 via a data path established by the second processor 120 between the data plane processing module 128 and the system memory 112. The control data is used for generation of downlink TBs and for scheduling the transmission of the downlink TBs on a downlink communication channel to the UEs in the cellular network. Similarly, the data plane processing module 128 receives uplink TBs from the L1 processing agent 132 via another data path and generates the uplink data packets.
The air interface scheduler 130 receives the control data from the data plane processing module 128 by way of a control path established by the second processor 120 between the data plane processing module 128 and the air interface scheduler 130. The air interface scheduler 130 further identifies quality of service (QoS) information for the UEs being serviced by the eNodeB according to the 3GPP specifications for LTE and LTE-advanced (LTE-A) standards. In another example, the air interface scheduler 130 identifies the QoS information based on the type of UEs in the cellular network being serviced by the eNodeB. The QoS information for a UE supporting third generation (3G) networks may vary from another UE supporting fourth generation (4G/LTE) networks. For example, the QoS information may include a minimum bandwidth to be provided to the UEs for the uplink and downlink communication channels. Such QoS information that is being determined by the air interface scheduler 130 is referred to as bearer QoS values. Based on a bearer QoS value and the control data, the air interface scheduler 130 generates a downlink transmission schedule for generating downlink TBs by data plane processing module 128 and for scheduling transmission of the downlink TBs via the downlink communication channel. The air interface scheduler 130 may also generate scheduling information for reception of uplink TBs that may be transmitted from the UEs via the uplink communication channel. Thus, the air interface scheduler 130 also generates an uplink transmission schedule for the uplink communication channel based on the bearer QoS value.
The first processor 118 is connected to the second processor 120 by way of the shared memory 122 for receiving the downlink TBs. A L1 processing agent 132 runs on the first processor 118. The downlink TBs are transmitted from the data plane processing module 128 to the L1 processing agent 132 via a data path established by the first and second processors 118 and 120. The L1 processing agent 132 performs processing for a L1 of the wireless protocol stack for the downlink TBs. The L1 processing agent 132 receives and processes the downlink TBs for generating downlink in-phase and quadrature-phase (I/Q) samples. The L1 processing agent 132 further receives the downlink and uplink transmission schedules via a control path established by the first and second processors 118 and 120 between the air interface scheduler 130 and the L1 processing agent 132 using the shared memory 122. The downlink I/Q samples are provided to the RFIC 108 for transmission on the downlink communication channel based on the downlink transmission schedule. For the uplink communication, uplink I/Q samples are received by the L1 processing agent 132 from the RFIC 108 based on the uplink transmission schedule. The L1 processing agent 132 processes the received uplink I/Q samples to generate the uplink TBs.
The DMA system 124 is connected to the first and second processors 118 and 120, and the shared memory 122 for enabling storage and retrieval of the uplink and downlink TBs, the uplink and downlink I/Q samples, and various parameters by the first and second processor 118 and 120 for L1 and L2 processing, respectively. Such parameters can include polynomial weights for digital pre-distortion. The shared memory 122 may be a random access memory (RAM) such as a dynamic RAM (DRAM), a static RAM (SRAM), or a double-data rate (DDR) memory.
The hardware accelerator 116 is connected between the first processor 118 and the RFIC 108. The hardware accelerator 116 executes a pre-defined set of instructions and enables processing of the uplink and downlink I/Q samples before transmission of the downlink I/Q samples and after reception of the uplink I/Q samples. The hardware accelerator 116 is any one of a multi-accelerator platform such as MAPLE, a digital front end (DFE) accelerator, or ICs programmed for computationally intensive functions. The baseband unit 106 may include multiple such accelerators (not shown). Accelerators such as cryptographic accelerators or packet processing accelerators may be included in an L2 sub-system of the baseband unit 106 that includes the second processor 120.
The RFIC 108 receives uplink analog RF signals from the UEs by way of the uplink communication channel and generates the uplink I/Q samples. The RFIC 108 further receives the downlink I/Q samples from the L1 processing agent 132 and generates downlink analog RF signals. The PA 110 is connected to the RFIC 108 for receiving and amplifying the downlink analog RF signals for transmission to the UEs over the downlink communication channel using the antenna 104.
The downlink and the uplink TBs are transmitted and received based on the downlink and uplink transmission schedules generated by the air interface scheduler 130 being executed on the second processor 120. The components of the baseband unit 106 may face several platform health problems such as overloading of the hardware accelerator 116, over-run of the DMA system 124, bandwidth overloading of the shared and system memories 122 and 112, and processing overload of the first processor 118 that occur in real-time, and hence are unforeseen. However, since the air interface scheduler 130 in the second processor 120 does not receive feedback regarding any real-time parameters associated with the aforementioned platform health problems, the downlink and uplink transmission schedules are not modified to address and remedy the platform health problems. Thus, even though the first processor 118 may be overloaded, the second processor 120 may schedule transmission of more downlink TBs by the first processor 118, thereby leading to overloading and shut-down of the first processor 118 and the baseband unit 106. Similarly, the hardware accelerator 116 or the DMA system 124 may malfunction and shut-down. Thus, the eNodeB may shut-down and go out of service. Since the real-time health parameters are not monitored by the air interface scheduler 130, the performance of the eNodeB is unstable and hence, the bandwidth provided to the UEs for the uplink and downlink communication channels may not meet the desired bearer QoS value as specified by the wireless protocol stack, or the 3G and 4G standards.
A known technique to overcome the aforementioned problem uses buffers at the end-points of the BTS and the IP gateway. The buffers measure a delay in transmission of a data packet between the BTS and the IP gateway. When the delay exceeds a predetermined threshold value, a value of a QoS parameter of a service provided by the BTS to the UE is downgraded. However, the aforementioned technique does not enable monitoring of the aforementioned platform health problems caused in a baseband unit of the BTS. Further, the aforementioned technique requires utilization of components external to the BTS such as the IP gateway, and hence, is not a feasible solution. Furthermore, due to stringent uptime requirements by LTE operators, the eNodeB is required to be highly stable and operational in 99.999% of the scenarios.
Therefore, it would be advantageous to have a baseband unit that monitors real-time parameters associated with platform health problems of the baseband unit and other peripheral devices of an eNodeB, remedies the platform health problems in real-time, prevents shut-down of various components of the baseband unit, prevents the eNodeB from going out of service, and maintains the desired bearer QoS value for the UEs being serviced.